Long Term Evolution, LTE, is a wireless communication system developed by the 3rd Generation Partnership Project, 3GPP. In LTE cell detection and initial synchronization are based on two synchronization signals, a Primary Synchronization Signal, PSS, and a Secondary Synchronization Signal, SSS. A single radio frame comprises two PSS/SSS sequences in LTE, and the two PSS/SSS sequences are with a periodicity of 5 ms.
One of the topics in LTE is device-to-device, D2D, communications and 3GPP is finalizing the specifications for certain D2D operations at the moment. In the context of D2D communications a Primary Device-to-Device Synchronization Signal, PD2DSS, corresponds to the PSS while a Secondary Device-to-Device Synchronization Signal, SD2DSS, corresponds to the SSS. Moreover, it has been agreed that there will be two PD2DSSs and two SD2DSSs in a single subframe with a periodicity of 40 ms for D2D communications.
Synchronization signals are also employed in other wireless cellular systems such as Wideband Code Division Multiple Access, WCDMA, and CDMA2000, for example. In addition to different wireless cellular systems, synchronization signals are used in several other wireless systems, such as, Wireless Local Area Network, WLAN, and Worldwide Interoperability for Microwave Access, WiMAX, systems as well.